Arctic amplification and their relation to regional warming

Abstract: Arctic amplification (AA) is defined as the enhanced warming of the surface temperatures in the Arctic region relative to the globe or Northern Hemisphere (NH) in response to external forcings. It is a prominent feature of the climate system. Various metrics have been used in studies to quantify AA, and this introduces a challenge when comparing studies due the differences in AA magnitudes. This study aims to compare these different metrics and investigate their relation to the regional surface temperature changes in the NH. Furthermore, the difference between metrics used to quantify the amplification of the Arctic region (60° - 90°N) were investigated along with their variations through time. A brief review of the processes causing AA is done, including both local and remote influences that may affect AA. A moving window of 11-years was applied to the surface air temperature (SAT) anomalies to reduce interannual variability. The regional SAT changes that contribute to the variations in the AA metrics were further investigated by correlating the AA metrics with the SAT in the NH (0 °- 90°N). The results show how temperature changes in the Arctic and NH varied through time from the years 1950-2021. This study also shows new results for the state of AA until 2021. Metrics using the ratio of the linear trends (A2), ratio of SAT variations (A3), and regression between the Arctic and NH SAT anomalies (A4) show similar variations in time, with a prominent increase and subsequent decrease of AA between 2000-2010. These metrics also show similar variations in time for the later years where there is a slight increase of Arctic Amplification Index (AAI) until 2016. The ratio of SAT anomalies between the Arctic and NH (A0) shows an overall similar temporal pattern as the previous three metrics but with smaller magnitude in the variations. The difference between the SAT anomalies between the Arctic and NH (A1) does not clearly show enhanced AA around 2003, but rather reflect a steady increase over time. Furthermore, defining AA as the ratio of SAT anomalies between the Arctic and NH sometimes leads to extreme values in the AA index which are found in metrics A0 and A2. The correlations show that A0 and A1 show similar correlations with SAT anomalies, with positive correlations in the North Atlantic Ocean, over a large part of Asia and on the western side of the North Pacific Ocean and along the western coast of North America. A2, A3, and A4 on the other hand show positive correlations over most of the NH, except for a patch of negative correlations in the North Pacific Ocean. This study provides data for the recent magnitude of AA using the different metrics, and some insight on the driving SAT changes in the NH on the AA.